1. Field of the Invention
The present invention relates to an ink jet printer that forms images on a recording sheet and the like by ejecting ink from nozzles.
2. Description of the Related Art
Conventional printers and other recording devices are provided with a recording head for forming images on a recording sheet. Normally, such recording heads are mounted in a carriage that moves along a widthwise direction of the recording sheet, and a flexible wiring board is connected to the recording head for driving the same. The flexible wiring board is in connection with a wiring plate, which is connected to a circuit provided to a main body of the recording device. With this configuration, the recording head is controlled through the flexible wiring board to perform printing.
Examples of this type of recording head include ink jet heads, dot impact heads, and thermal transfer heads. Among these, the ink jet head is known to have a relatively simple construction, perform high-speed printing, and achieve high quality.
As shown in FIG. 1, an example of this type of ink jet printer includes a head unit provided an ink cartridge 1, a head holder 2, and an ink jet head 3 attached to the head holder 2.
The ink cartridge 1 is formed of a resin material and includes a porous member chamber 4 and an ink chamber 5. The porous member chamber 4 accommodates a porous member filled with ink. The ink chamber 5 is separated from the porous member chamber 4 and formed with an ink supply inlet 6. The head holder 2 is also formed of a resinous material and accommodates the ink cartridge 1. The head holder 2 is formed with a communicating hole 7 at a position confronting the ink supply inlet 6 of the ink chamber 5.
The ink jet head 3 includes an actuator 8 and a manifold 9. The actuator 8 is formed of a piezoelectric ceramic material and is formed with a plurality of ejection channels (not shown). The actuator 8 and the manifold 9 are joined by a UV adhesive after positioning the two at a prescribed position in relation to each other, and a silicon type potting material is formed around the ink channels to form a seal.
The manifold 9 is formed of a resin and includes an ink introducing unit 11 formed with an ink introducing channel 10 connected to the ink supply inlet 6 and an ink supply unit 13 formed with an ink supply channel 12 for distributing ink to the ejection channels of the actuator 8.
A sealing member 14 formed of a ring-shaped elastic material is adhesively fixed to the inner surface of the communicating holes 7. By inserting the ink introducing unit 11 through the sealing member 14, the ink introducing channel 10 is connected to the ink supply inlet 6 via the sealing member 14.
A base plate 15 formed of a metal material is interposed between the sealing member 14 and the ink supply unit 13. The base plate 15 serves to set the ink jet head 3 at a reference position. By fixing the ink supply unit 13 to the base plate 15, the ink jet head 3 becomes supported on the base plate 15. The base plate 15 is adhesively fixed to the head holder 2 via the sealing member 14.
The actuator 8 is provided with an ejection energy generating unit (not shown). A chip-on-board (COB) 17, on which a drive circuit is mounted, is connected to the ejection energy generating unit via a flexible wiring board 16 for generating pulse signals to drive the actuator 8 so as to eject ink droplets from the ejection channels.
When the head holder 2 is mounted in a carriage (not shown), contact points of the COB 17 contact contact points of a wiring plate provided on the carriage. A lock member applies pressure to the contact points of the head holder 2 and the carriage, and fixes these two components so as to maintain both components in a state of contact. As is well known in the art, the wiring plate on the carriage connects to a control circuit board of the recording device via a flexible cable.
Ink in the ink cartridge 1 is supplied via the ink supply inlet 6 and the ink introducing channel 10 of the manifold 9 to the ink supply channel 12. From the ink supply channel 12, the ink is distributed to each ejection channel of the actuator 8. The ejection energy generating unit changes the capacity of each ejection channel based on ejection pulse signals emitted from the COB 17. When the capacity of the ejection channel is reduced, an ink droplet is ejected from the corresponding nozzle. When the capacity is increased, ink is reintroduced into the ejection channel. By performing these operations repeatedly, a prescribed image is formed on recording sheet.
In this type of ink jet head 2, it is necessary for the lock member on the head holder 2 to firmly press the COB 17 in order to ensure a reliable connection between the COB 17 and the wiring plate on the carriage. However, the head holder 2 can warp under the strong pressure. Also, an elastic member formed of rubber or the like that pushes the wiring plate on the carriage toward the COB 17 applies a reaction force on the contacts to the COB 17. This can potentially cause positional deviation in the base plate 15 that is adhesively fixed to the head holder 2 or the manifold 9 and the actuator 8 supported on the base plate 15. When such positional deviations occur, the nozzles of the actuator 8 are also forced out of position, making it impossible to achieve a sufficient print quality.
Also, the UV adhesive used for joining the manifold 9 and the actuator 8 is cured by exposure to ultraviolet light. After hardening, the adhesive is relatively flexible. The silicon potting material also has a relatively flexible quality, like an elastic rubber, after hardening.
That is, the bond between the manifold 9 and the actuator 8 is not very firm. Accordingly, the positional relationship between the manifold 9 and the actuator 8 could be thrown off by heat or external forces applied during processes that follow assembly of the ink jet head 3, and also by pressure from the ink cartridge 1 or from a protective cap during purging operations or when the printer is not being used. Should such deviation in the position occur, air bubbles may become trapped in the gap between the manifold 9 and the actuator 8 when using the ink jet printer. Since the surface area in which the air bubbles can contact the silicon potting material is large, the trapped air bubbles can grow and result in ejection problems after the printer has been at rest.
Also, these deviations can offset the position of the nozzles in relation to the base plate 15, making it impossible to achieve satisfactory printing quality.
Further, while the manifold 9 is formed of a resin, the base plate 15 is formed of a metal material having a considerably different linear expansion coefficient (about 9 times larger). As a result, changes in temperature can cause peeling and cracking to occur between the manifold 9 and the base plate 15, causing positional deviation of the nozzles in relation to the base plate 15. In this case, it is not possible to achieve satisfactory printing quality.
Further, the ink introducing unit 11 of the manifold 9 is connected to the ink supply inlet 6 of the ink cartridge 1 via the communicating holes 7 of the head holder 2. Accordingly, the position of the nozzles in the actuator 8 is easily affected by the ink cartridge 1 and the head holder 2. Pressure from the ink cartridge 1 directly affects the manifold 9. This type of pressure can easily cause positional deviations of the nozzles in relation to the base plate 15.
The above described head unit also includes a filter 18 provided on the ink inlet of the manifold 9 for removing foreign matter, air bubbles, and the like that can generate problems in ink ejection. The filter 18 has a mesh diameter smaller than the diameter of the nozzles.
During the assembly, the filter 18 is first welded to the ink inlet of the manifold 9, and then the actuator 8 is fixed to the manifold 9.
After the assembly, various ejection tests are performed to determine whether ink is properly ejected without the nozzles becoming clogged with foreign matter. In these ejection tests, water is introduced through the filter 18 into the manifold 9 and actuator 8. If the nozzles are not clogged with foreign matter, the water will flow out of the nozzles in a straight line. However, if the nozzles are clogged with foreign matter, water will come out of the nozzles at an angle. When water comes out of the nozzles at an angle, the ink jet head 3 is considered a reject and is not passed on to subsequent processes.
Ink jet heads 3 that are rejected in these ejection tests can be reused, provided the foreign matter is removed from the nozzles. However, it is not possible to clean the nozzles by forcing water rear through in the reverse direction when the filter 18 is welded in the manifold 9. Hence, the ink jet head 3 must be disposed.
In light of this problem, there have been proposals for an ink jet head in which the head is screwed to a head holder in order to fix the ink jet head in a reference position. The head holder is also provided with a member that supports a filter. When nozzles become clogged with foreign matter, the ink jet head is removed from the head holder and water is force rearward from the nozzles. Subsequently, the head holder is reattached and the ink jet head can be reused.
However, this method is inconvenient in that it requires considerable effort. After satisfactorily fixing the ink jet head at a reference position with the head holder, the head holder must be temporarily removed and reattached. When reattaching the head holder, it is necessary to reset the head holder to its original reference position and firmly fix the head holder in position with screws. Moreover, after repeatedly removing and reattaching the head holder with the screws, the screws begin to lose their ability to firmly fix the head holder and the inkjet head must be disposed.
Also, the circuit board mounts the circuit element on one surface and a radiator attached to the other surface. Because the radiator is produced by punching an aluminum alloy material, burrs are formed on the edges of the radiator.
If such a radiator with burrs formed on the edges is attached to the circuit board with the burrs opposing the circuit board, the burrs can scratch a pattern in the circuit board, causing electrical disconnections or shorts. If the radiator is attached to the circuit board with the burrs facing outward, the burrs can scratch a flexible printed circuit board connected to the circuit board, causing wiring breaks and shorts also.
Further, since adhesive is applied to the entire surface of the radiator when attached to this type of conventional circuit board, the circuit board can be warped by differences in the linear expansion coefficient between the radiator and the circuit board.
Also, in this type of ink jet recording head, the ink supply channel 12 and the like are formed by fixing a center plate of the actuator 8 to the manifold 9. A space, such as a groove or depression, is formed between the center plate and the manifold 9 along the outside of the ink supply channel 12 and the like. When fixing the center plate to the manifold 9, a sealing agent is introduced into the space by inserting a fine pipe dispenser therein, so as to prevent ink leakage and also to prevent air from entering the ink in the ink introducing channel 10 and the ink supply channel 12. The fine pipe dispenser helps maintaining the fluidity of the sealing agent.
However, when the space is deep, the sealing agent blocks the entrance to the space, trapping air bubbles that have no means of escape, so that the sealing agent does not reach all the way to the innermost part of the space. Also, because the ink jet head 3 is small in size, the space is even smaller. It is difficult to insert the dispenser into such a small space. This increases the possibility of trapped air bubbles. The air bubbles trapped in the space in this manner makes sealing capacity insufficient, generating ink leakage and allowing small amounts of external air into ink in the ink supply channel 12 and the like.
Extremely small air bubbles contained in the ink within the ink supply channel 12 have little effect on ink ejection. However, when external air enters through miniature gaps between the center plate and the manifold 9, air bubbles are formed in the ink and become trapped in the ink supply channel 12 and the ejection channels, thereby generating problems in ink ejection.
Usually, a sealing agent having a low air permeability is used to seal the contact points between the center plate and the manifold 9. Such sealing agents ensure to prevent air from entering the ink supply channel 12. Most sealing agents with a low air permeability require curing by heat and firmly fix the center plate to the manifold 9.
However, the linear expansion coefficient of the material used in the center plate and the manifold 9 is often different. If these two members are adhered firmly to each other, changes in ambient temperature and temperature changes when manufacturing the ink jet head 3 can generate warping or cracking between the center plate and the manifold 9 due to the different linear expansion coefficients. Such warping or cracking greatly increases the amount of external air that enters.
Since the sealing agent directly contacts ink that leaks through gaps between the center plate and the manifold 9, it is necessary for the sealing agent to have a high resistance to ink. However, sealing agents having a high resistance to ink generally have a high air permeability at the same time.
When installing a filter in two joint members having an ink channel, such as the filter 18 between the ink cartridge 1 and the ink jet head 3 jointed together, the filter can be preinstalled in the joint members by heat, welding, or the like, and the two joint members are joined together by ultrasonic welding. In this case, the ultrasonic waves vibrate the center portion of the filter, causing the outer portion of the filter to peel from the joint members. Rather than peeling, in some cases the vibrations cause the center portion of the filter to contact the inner side of the ink channel and become fused thereon. If the filter is maintained in this deformed state, the effective surface area of the filter is reduced, thereby hindering the supply of ink and greatly affecting the printing result.
It is necessary to increase the amount of ink supplied per unit time from the ink cartridges when increasing the number and density of ink channels in the ink jet head. Also, the filter pores (miniature openings in the filter) are decreased in size to raise the filtration precision, it is necessary to enlarge the effective area of the filter. Since the possibility of foreign matter entering the ink is largest when connecting or detaching the cartridge to the ink jet head, a filter is generally installed on the ink jet head at the point of connection. However, it is difficult to seal the connection point between the ink jet head and ink cartridge when the filter has a large effective area. This potentially results in ink leakage and the generation of air bubbles in the ink channels from external air entering therein. Moreover, as the surface area of the filter becomes larger, the chance for dust and other foreign matter from becoming deposited on the filter grows larger when the ink cartridge is in a detached state.
It is conceivable to install the filter in the ink channels separated a sufficient distance from the point of connection, enabling the connection point to be reduced without concern for the size of the filter. However, in this configuration, ink may leak from the nozzles when the ink cartridge is removed from the ink jet head. Usually, a negative pressure generator, such as a porous foam in the ink cartridge, applies a negative pressure to the ink that is supplied to the ink jet head and prevents ink from leaking from the nozzles. However, atmospheric pressure works on the ink in the ink jet head when the ink cartridge is not connected thereto. At this time, when ink droplets become deposited around even one of the plurality of nozzles, the meniscus of ink in the nozzle becomes broken, allowing ink to flow due to a water head difference H (see FIG. 6) between the connection part and the nozzle. In other words, ink leakage occurs. Leaking ink spreads around the other nozzles, affecting their ejecting properties, such as bending the direction of ink ejection during an ejection operation, further soiling the inside of the main recording device with ink, and decreasing the quality of the image formed on the recording paper.